Surface Tension Flows inside Surfactant-Added Poly(dimethylsiloxane) Microstructures with Velocity-Dependent Contact Angles

Surface Tension Flows inside Surfactant-Added Poly(dimethylsiloxane) Microstructures with Velocity-Dependent Contact Angles

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Filling of purple and black wigs liquid samples is realized in a microfluidic device with applications including analytical systems, biomedical devices, and systems for fundamental research.The filling of a disk-shaped polydimethylsiloxane (PDMS) microchamber by liquid is analyzed with reference to microstructures with inlets and outlets.The microstructures are fabricated using a PDMS molding process with an SU-8 mold.

During the filling, the motion of the gas-liquid interface is determined by the competition among inertia, adhesion, and surface tension.A single ramp model with velocity-dependent contact angles is implemented for the accurate calculation of surface tension forces in a three-dimensional volume-of-fluid based model.The effects of the parameters of this functional form are investigated.

The influences of non-dimensional parameters, such as the Reynolds number and the Weber number, both determined by the inlet velocity, on the flow characteristics are also examined.An oxygen-plasma-treated PDMS substrate is utilized, and the microstructure is modified to be hydrophilic.Flow experiments are conducted into both hydrophilic and hydrophobic PDMS microstructures.

Under a shibori dot fabric hydrophobic wall condition, numerical simulations with imposed boundary conditions of static and dynamic contact angles can successfully predict the moving of the meniscus compared with experimental measurements.However, for a hydrophilic wall, accurate agreement between numerical and experimental results is obvious as the dynamic contact angles were implemented.